The present invention relates to a method and a device for monitoring the functionality of a device for variably adjusting the cylinder compression ratio in a reciprocating internal combustion engine.
It is desirable to adjust the cylinder compression ratios to the operating states of a reciprocating internal combustion engine, especially to the load under which the engine is running. For if, e.g., the compression can be increased at low load and decreased at full load (throttle), considerable reductions in fuel consumption can be achieved. By variably adjusting the compression ratio, as is known, for example, from German Patent Application No. DE 198 44 200 or German Patent No. DE 197 03 948, a low compression ratio (e.g., e=8) is advantageously set at full throttle to prevent knocking that is damaging to the engine. In the case of a highly loaded engine, this produces a high specific full-throttle torque. At part throttle, the compression ratio is increased (e.g., e=15). This allows considerable improvements in efficiency in comparison with naturally aspirated engines and conventional compression engines. Devices for variably adjusting the cylinder compression ratio are known from the two mentioned documents, DE 197 03 948 and DE 198 44 200, where the effective length of the connecting rods, which join the pistons in the cylinders to the crankshaft, can be varied. If a defect occurs on a device, with which an internal combustion engine is equipped, and whose function is to variably adjust the cylinder compression ratio, then this would disadvantageously lead to an increase in fuel consumption. In order to avoid this disadvantage, the present invention is based on the object of providing a method and a device, by which the functionality of the device for variably adjusting the cylinder compression ratio is monitored, and by which a malfunction or a defect of this device can be detected as quickly as possible.
The above-mentioned object is achieved in that an engine operating parameter, which reacts to a change in the cylinder compression ratio, is ascertained both before and after controlling the device for changing the cylinder compression ratio; and in that both values of the engine operating parameter are compared to each other, in order to determine if the engine operating parameter has changed; a change of the engine operating parameter being an indication that the device for variably adjusting the cylinder compression ratio is functioning correctly. The present invention allows a device for variably adjusting the cylinder compression ratio to be monitored for functionality, without requiring additional sensors for measuring the cylinder compression ratio.
Therefore, during the deceleration of the internal combustion engine, it is useful to control the device for changing the cylinder compression ratio and to ascertain the engine operating parameter before and after controlling this device, in order to carry out the functionality monitoring (implement the watchdog functions).
Furthermore, it is useful to control the device for: changing the cylinder compression ratio in a manner allowing the compression ratio of each cylinder to be adjusted individually, and it is useful to ascertain the engine operating parameter before and after controlling each individual cylinder, in order to carry out the functionality monitoring for each cylinder.
The running irregularity, combustion-chamber pressure, intake-manifold pressure, or engine torque is suitable as the engine operating parameter for monitoring the variable compression ratio.